The US President has said that a coronavirus vaccine will be ready “long before the end of the year”. However, Dr Stephen Hahn, US Food and Drug Administration (FDA) Commissioner, has cast doubt on Mr Trump’s plans.
On Sunday, Dr Hahn said: “I can’t predict when a vaccine will be available.”
He added that a vaccine development would be “based upon the data and science”.
Dr Hahn is a member of the White House coronavirus task force.
Speaking to ABC News, Dr Hahn said “we are seeing unprecedented speed for the development of a vaccine”, but did not confirm when it would be ready.
He added: “Our solemn promise to the American people is that we will make a decision based upon the data and science on a vaccine, with respect to the safety and effectiveness of that vaccine.”
Mr Trump said at the Independence Day address: “I want to send our thanks to the scientists and researchers around the country, and even around the world, who are at the forefront of our historic effort to rapidly develop and deliver life-saving treatments and ultimately a vaccine.
“We are unleashing our nation’s scientific brilliance and we’ll likely have a therapeutic and/or vaccine solution long before the end of the year.”
In June, the head of the World Health Organization (WHO), Dr Tedros Adhanom warned scientists that they may never be able to create an effective vaccine against the coronavirus.
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The total number of confirmed Covid-19 cases in the US is just over 2.9 million.
Infections have reportedly been increasing rapidly in the western and southern states.
Speaking to CNN, Dr Hahn said he would not respond to President Trump’s claim that 99 percent of coronavirus infections were “totally harmless”.
Dr Hahn said: “I’m not going to get into who is right and who is wrong.”
There are reportedly around 120 vaccine programmes currently taking place for the coronavirus.
In the UK, Imperial College and Oxford University have both started human trails of their vaccines.
Last week Dr Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said that the safety and effectiveness of a Covid-19 vaccine should be known by “early winter” in the US.
He added that trails for some vaccines would be entering the latter stages of testing this month.
He said: “We may be able to at least know whether we are dealing with a safe and effective vaccine by the early winter, late winter, beginning of 2021.”
In the US 132 thousand people have reportedly died from the coronavirus.